Basically, you screw one or two metal brackets into your wall and place a hardcover book on top. The secret to creating the "floating" illusion is to cut slits into the book jacket before fitting the book into place on the wall. Here are more detailed instructions on how to do that.

Worried about damaging the book cover? No problem! You can use velcro to make the bracket sit between the internal pages of the book and the back cover. The velcro prevents the back flap from hanging down while concealing the bracket, so your bookshelf is "invisible."